The third generation partnership project (3GPP) high speed uplink packet access (HSUPA) employs a mechanism known as “happy bit” to allow a wireless transmit/receive unit (WTRU) to indicate to the network whether the uplink data rate allocated to the WTRU is sufficient or not given the amount of data in the WTRU buffer. The happy bit is included in an enhanced dedicated channel (E-DCH) dedicated physical control channel (E-DPCCH) for every E-DCH transmissions.
A radio resource control (RRC) entity configures a medium access control (MAC) entity with the duration Happy_Bit_Delay_Condition. The WTRU evaluates the current grant relative to the total E-DCH buffer status (TEBS) during this duration after application of an E-DCH transport format combination (E-TFC) selection. In accordance with the 3GPP specification 25.321 V8.2.0, for every E-DCH transmission, the happy bit is set to “unhappy” if the following three criteria are met:
(1) The WTRU is transmitting as much scheduled data as allowed by the current Serving_Grant in E-TFC selection;
(2) The WTRU has enough power available to transmit at a higher data rate; and
(3) Based on the same power offset as the one selected in E-TFC selection to transmit data in the same transmission time interval (TTI) as the happy bit, TEBS would require more than Happy_Bit_Delay_Condition ms to be transmitted with the current Serving_Grant.times.the ratio of active processes to the total number of processes.
If the above three criteria are not met, the happy bit shall be set to “happy.” The received happy bit may be used by the network to determine whether the serving grant should be increased, decreased, or left unchanged.
In accordance with the 3GPP specification, the WTRU will only set the happy bit to “unhappy” if the WTRU has sufficient transmission power to include at least one additional radio link control (RLC) protocol data unit (PDU) in an E-TFC. In other words, the WTRU sets the happy bit to “unhappy” only if there is an E-TFC that may accommodate one additional RLC PDU compared to the one used when the happy bit is determined and the E-TFC is in a “supported state.” This restriction has been introduced to prevent the WTRU from requesting a higher data rate from the network while the WTRU would anyway be unable to increase its data rate due to power restrictions.
With the introduction of flexible RLC PDU size and segmentation at the MAC layer for the HSUPA in 3GPP Release 8, restriction that the WTRU has to be capable of transmitting at least one additional RLC PDU in an E-TFC is needlessly restrictive because the WTRU may increase the data rate by transmitting a segment of an additional RLC PDU or just increase the size of the RLC PDU. With this restriction the WTRU will not set the happy bit to “unhappy” even though the WTRU can increase the data rate by transmitting a fraction of an additional RLC PDU or by increasing the size of subsequent RLC PDUs. Thus, under the conventional 3GPP specification, the uplink data rate is not maximized.
Under the current 3GPP specification, if the serving grant becomes too small to allow transmission of a single PDU from any scheduled MAC-d flow or if the serving grant is too small to allow transmission of a single PDU from any scheduled MAC-d flow and TEBS becomes larger than zero, the transmission of scheduling information is triggered. With the introduction of MAC segmentation for the HSUPA, it is unlikely that the WTRU is unable to transmit any data when the serving grant falls below a certain value because with the introduction of MAC segmentation the WTRU may always be able to transmit a segment of an RLC PDU even if the grant is too small to allow the transmission of a full RLC PDU. Therefore, the above scheduling information triggering criterion is not desirable and may result in excessive transmission of the scheduling information.